I am sorry to say that it looks like the sensor itself is going. To fix it would require a whole new sensor - you are better off buying a new cam..[no]
Simliar thing happened to my Olympus E-510 within 6 months of having & because i bought the camera of Ebay, Olympus wouldn't honnour the warrenty because the actual camera thou brand new was a grey import. [cursing]